I definitely don't always ride shoulders in line. It depends on what I'm trying to accomplish. The PureBoarding guys like massive rotation from what I recall of a clinic. Some people like to have rigidly locked boots, others ride in "walk" mode. Once upon a time I rode with knees jammed together, now they're neutral.
Unless you're trying to get into racing, do some experimentation because it's an art. Watch some carving videos and try something new each time.
Knowing *how* to snowboard, you'll have an easy transition.